Streptavidin-based nanostructures : from bulk to surface-confined assembly studies

Self-assembly, the ability of disordered units to spontaneously organize themselves into high-order structures via non covalent bonds, is a physical principle allowing nanostructures to be created from the bottom-up, extending nano-order to macroscales.
This thesis was dedicated to program the self-organization of mature wild-type streptavidin by using linear tetrabiotinylated and trifurcated hexabiotinylated connectors.
Self-organization studies in bulk solution demonstrated that streptavidin combined with a linear tetrabiotinylated connector spontaneously assembled into a one-dimensional streptavidin-based block copolymer. In the presence of calcium ions, the fibrils formed bundles that served as a template for the nucleation, the growth and the assembling of calcite microcrystals. This hierarchical self-assembly process yielded millimeter-sized one-dimensional mineralized protein matrices. Both mineralized and naked one-dimensional streptavidin-based block co- polymers were imaged by electron microscopy.
With the aim of obtaining well-defined and monodisperse nanostructures, a step-by- step assembly approach was investigated. Designed mixed bis-biotinylated monolayers on gold were used to anchor streptavidin, which was successively exposed to linear tetrabiotinylated or trifurcated hexabiotinylated connectors and streptavidin. The stepwise elongation process was followed in situ by surface plasmon resonance and quartz crystal microbalance with dissipation monitoring. The size-controlled immobilized streptavidin-based fibrils were scrutinized by atomic force microscopy in the hydrated state.